news

academic biography

I did my schooling at St. Columba's in New Delhi (1971-1983). I started life as a student of Japanese, and worked as a patent translator in Osaka, Japan (1990-92). I got interested in linguistics during this period, and eventually completed a PhD in linguistics from Ohio State. My PhD advisors at OSU were Rick Lewis, and later, after Rick left for Michigan, Shari Speer.

research

My group develops models of human sentence comprehension, focusing on both impaired and unimpaired populations. Statistics is the basis for everything that we do, so we are also interested in statistical theory and practice.
My curriculum vitae.

teaching

Note:
I teach several courses on statistical data analysis. There are two tracks.
One is a non-math oriented version (summer semester, Introduction to statistical data analysis); this course gives a first, non-technical introduction to statistical analysis and is intended for MSc Linguistics, EMCL, IECL, and IDEALAB students, who may never need to do anything beyond a paired t-test. The second track is a more technically demanding introduction and is focused on linear mixed modeling. This is a sequence of three courses: Foundations of Mathematics (winter), Linear Modeling (summer), and Bayesian Data Analysis (winter). This three-course sequence spanning three semesters (which should be taken in order) covers all the statistical tools needed in psycholinguistics and linguistics. All courses rely on R, which is taught along the way. From 2015, a precondition to my accepting you as a PhD student (as primary advisor) is that you agree to take this three-course sequence (testing out of specific courses is possible if you know the material already).

research articles

published, accepted, in press

Traxler et al. (1998) found that ambiguous sentences are read faster than their unambiguous counterparts. This so-called ambiguity advantage has presented a major challenge to classical theories of human sentence comprehension (parsing) because its most prominent explanation, in the form of the unrestricted race model (URM), assumes that parsing is non-deterministic. Recently, Swets et al. (2008) have challenged the URM. They argue that readers strategically underspecify the representation of ambiguous sentences to save time, unless disambiguation is required by task demands. When disambiguation is required, however, readers assign sentences full structure — and Swets et al. provide experimental evidence to this end. On the basis of their findings they argue against the URM and in favor of a model of task-dependent sentence comprehension.
We show through simulations that the Swets et al. data does not constitute evidence for task-dependent parsing because it can be explained by the URM. However, we provide decisive evidence from a German self-paced reading study consistent with Swets et al.’s general claim about task-dependent parsing. Specifically, we show that under certain conditions, ambiguous sentences can be read more slowly than their unambiguous counterparts, suggesting that the parser may create several parses, when required. Finally, we present the first quantitative model of task-driven disambiguation which subsumes the URM, and show that it can explain both Swets et al.’s results and our findings.

Individuals with agrammatic Broca's aphasia experience difficulty when processing reversible non-canonical sentences. Different accounts have been proposed to explain this phenomenon. The Trace Deletion account attributes this deficit to an impairment in syntactic representations, whereas others propose that the underlying structural representations are unimpaired, but sentence comprehension is affected by processing deficits, such as slow lexical activation, reduction in memory resources, slowed processing and/or intermittent deficiency, among others. We test the claims of two processing accounts, slowed processing and intermittent deficiency, and two versions of the Trace Deletion Hypothesis, in a computational framework for sentence processing implemented in ACT-R. The assumption of slowed processing is operationalized as slow procedural memory, so that each processing action is performed slower than normal, and intermittent deficiency as extra noise in the procedural memory, so that the parsing steps are more noisy than normal. We operationalize the Trace Deletion Hypothesis as an absence of trace information in the parse tree. To test the predictions of the models implementing these theories, we use the data from a German sentence-picture matching study reported in Hanne-EtAl-2011. The data consists of offline (sentence-picture matching accuracies and response times) and online (eye fixation proportions) measures. From among the models considered, the model assuming that both slowed processing and intermittent deficiency are present emerges as the best model of sentence processing difficulty in aphasia. The modeling of individual differences suggests that, if we assume that patients have both slowed processing and intermittent deficiency, they have them in differing degrees.

An English double-embedded relative clause from which the middle verb is omitted can often be processed more easily than its grammatical counterpart, a phenomenon known as the grammaticality illusion. This effect has been found to be reversed in German, suggesting that the illusion is language specific rather than a consequence of universal working memory constraints. We present results from three self-paced reading experiments which show that Dutch native speakers also do not show the grammaticality illusion in Dutch, whereas both German and Dutch native speakers do show the illusion when reading English sentences. These findings provide evidence against working memory constraints as an explanation for the observed effect in English. We propose an alternative account based on the statistical patterns of the languages involved. In support of this alternative, a single recurrent neural network model that is trained on both Dutch and English sentences indeed predicts the cross-linguistic difference in grammaticality effect.

Comprehension of non-canonical sentences can be difficult for individuals with aphasia (IWA). It is still unclear to which extent morphological cues like case-marking or verb inflection may influence IWA’s performance or even help to override deficits in sentence comprehension. Until now, studies have mainly used offline methods to draw inferences about syntactic deficits and, so far, only a few studies have looked at online syntactic processing in aphasia. We investigated sentence processing in German IWA by combining an offline (sentence-picture matching) and online (eye-tracking in the visual-world paradigm) method. Our goal was to determine whether IWA are capable of using inflectional morphology (number-agreement markers on verbs and case markers in noun phrases) as a cue to sentence interpretation. We report results of two visual-world experiments using German reversible SVO and OVS sentences. In each study, there were eight IWA and 20 age-matched controls. Experiment 1 targeted the role of case-morphology, while Experiment 2 looked at processing of number-agreement cues at the verb in case-ambiguous sentences. IWA showed deficits in using both types of morphological markers as a cue to non-canonical sentence interpretation and the results indicate that in aphasia, processing of case-marking cues is more vulnerable as compared to verb-agreement morphology. However, the online data revealed that IWA are in principle capable of successfully computing morphological cues, but the integration of morphological information is delayed as compared to age-matched controls. Furthermore, we found striking differences between controls and IWA regarding subject-before-object parsing predictions. While in case-unambiguous sentences IWA showed evidence for early subject-before-object parsing commitments, they exhibited no straightforward subject-first bias in case-ambiguous sentences, although controls did so for ambiguous structures. IWA delayed their parsing decisions in case-ambiguous sentences until unambiguous morphological information, such as a subject-verb-number-agreement cue, was available. We attribute the differential results for processing of case and agreement markers to differences in the degree of reliability of both morphological cues. We ascribe our findings for erroneous processing of case-unambiguous sentences in aphasia to late parsing commitments and failures in integrating case cues on time. For processing of case-ambiguous sentences in aphasia, we suggest that IWA adopt a wait-and-see strategy and make parsing commitments only when the agreement cue at the verb prompts a particular sentence structure. Our results for IWA further point to deficits in predictive processes during sentence comprehension.

Chinese relative clauses are an important test case for pitting the predictions of expectation-based accounts against those of memory-based theories. The memory-based accounts predict that object relatives are easier to process than subject relatives because, in object relatives, the distance between the relative clause verb and the head noun is shorter. By contrast, expectation-based accounts such as surprisal predict that the less frequent object relative should be harder to process. In previous studies on Chinese relative clause comprehension, local ambiguities may have rendered a comparison between relative clause types uninterpretable. We designed experimental materials in which no local ambiguities confound the comparison. We ran two experiments (self-paced reading and eye-tracking) to compare reading difficulty in subject and object relatives which were placed either in subject or object modifying position. The evidence from our studies is consistent with the predictions of expectation-based accounts but not with those of memory-based theories.

In explicit memory recall and recognition tasks, elaboration and contextual isolation both facilitate memory performance. Here, we investigate these effects in the context of sentence processing: targets for retrieval during online sentence processing of English object relative clause constructions differ in the amount of elaboration associated with the target noun phrase, or the homogeneity of superficial features (text color). Experiment 1 shows that greater elaboration for targets during the encoding phase reduces reading times at retrieval sites, but elaboration of non-targets has considerably weaker effects. Experiment 2 illustrates that processing isolated superficial features of target noun phrases—here, a green word in a sentence with words colored white—does not lead to enhanced memory performance, despite triggering longer encoding times. These results are interpreted in the light of the memory models of Nairne, 1990, 2001, 2006, which state that encoding remnants contribute to the set of retrieval cues that provide the basis for similarity-based interference effects.

Expectation-driven facilitation (Hale, 2001; Levy, 2008) and locality-driven retrieval difficulty (Gibson, 1998, 2000; Lewis &
Vasishth, 2005) are widely recognized to be two critical factors in incremental sentence processing; there is accumulating
evidence that both can influence processing difficulty. However, it is unclear whether and how expectations and memory
interact. We first confirm a key prediction of the expectation account: a Hindi self-paced reading study shows that when an
expectation for an upcoming part of speech is dashed, building a rarer structure consumes more processing time than
building a less rare structure. This is a strong validation of the expectation-based account. In a second study, we show that
when expectation is strong, i.e., when a particular verb is predicted, strong facilitation effects are seen when the appearance
of the verb is delayed; however, when expectation is weak, i.e., when only the part of speech “verb” is predicted but a
particular verb is not predicted, the facilitation disappears and a tendency towards a locality effect is seen. The interaction
seen between expectation strength and distance shows that strong expectations cancel locality effects, and that weak
expectations allow locality effects to emerge.

Recent research has shown that brain potentials time-locked to fixations in natural reading can be
similar to brain potentials recorded during rapid serial visual presentation (RSVP). We attempted
two replications of Hagoort, Hald, Bastiaansen, and Petersson (2004) to determine whether this
correspondence also holds for oscillatory brain responses. Hagoort et al. reported an N400 effect
and synchronization in the theta and gamma range following world-knowledge violations. Our
first experiment (n=32) used RSVP and replicated both the N400 effect in the event-related
potentials (ERP) and the power increase in the theta range in the time-frequency domain. In the
second experiment (n=49), participants read the same materials freely while their eye movements
and their EEG were monitored. First fixation durations, gaze durations, and regression rates were
increased, and the ERP showed an N400 effect. An analysis of time-frequency representations
showed synchronization in the delta range (1–3 Hz) and desynchronization in the upper alpha
range (11–13 Hz) but no theta or gamma effects. The results suggest that oscillatory EEG
changes elicited by world-knowledge violations are different in natural reading and RSVP. This
may reflect differences in how representations are constructed and retrieved from memory in the
two presentation modes.

Scanpaths have played an important role in classic research on reading behavior. Nevertheless, they have largely been neglected in later research perhaps due to a lack of suitable analytical tools. Recently, von der Malsburg and Vasishth (2011) proposed a new measure for quantifying differences between scanpaths and demonstrated that this measure can recover effects that were missed with the traditional eyetracking measures. However, the sentences used in that study were difficult to process and scanpath effects accordingly strong. The purpose of the present study was to test the validity, sensitivity, and scope of applicability of the scanpath measure, using simple sentences that are typically read from left to right. We derived predictions for the regularity of scanpaths from the literature on oculomotor control, sentence processing, and cognitive aging and tested these predictions using the scanpath measure and a large database of eye movements. All predictions were confirmed: Sentences with short words and syntactically more difficult sentences elicited more irregular scanpaths. Also, older readers produced more irregular scanpaths than younger readers. In addition, we found an effect that was not reported earlier: Syntax had a smaller influence on the eye movements of older readers than on those of young readers. We discuss this interaction of syntactic parsing cost with age in terms of shifts in processing strategies and a decline of executive control as readers age. Overall, our results demonstrate the validity and sensitivity of the scanpath measure and thus establish it as a productive and versatile tool for reading research.

A general fact about language is that subject relative clauses are easier to process than object relative clauses. Recently, several self-paced reading studies have presented surprising evidence that object relatives in Chinese are easier to process than subject relatives. We carried out three self-paced reading experiments that attempted to replicate these results. Two of our three studies found a subject-relative preference, and the third study found an object-relative advantage. Using a random effects Bayesian meta-analysis of fifteen studies (including our own), we show that the overall current evidence for the subject-relative advantage is quite strong (approximate posterior probability of a subject-relative advantage given the data: 78–80%). We argue that retrieval/integration based accounts would have difficulty explaining all three experimental results. These findings are important because they narrow the theoretical space by limiting the role of an important class of explanation—retrieval/integration cost—at least for relative clause processing in Chinese.

We explore the interaction between oculomotor control and language comprehension on the sentence level using two well-tested computational ac- counts of parsing difficulty. Previous work (Boston, Hale, Vasishth, & Kliegl, 2011) has shown that surprisal (Hale, 2001; Levy, 2008) and cue-based mem- ory retrieval (Lewis & Vasishth, 2005) are significant and complementary predictors of reading time in an eyetracking corpus. It remains an open question how the sentence processor interacts with oculomotor control. Using a simple linking hypothesis proposed in Reichle, Warren, and McConnell (2009), we integrated both measures with the eye movement model EMMA (Salvucci, 2001) inside the cognitive architecture ACT-R (Anderson et al., 2004). We built a reading model that could initiate short “Time Out
regressions” (Mitchell, Shen, Green, & Hodgson, 2008) that compensate for slow postlexical processing. This simple interaction enabled the model to predict the re-reading of words based on parsing difficulty. The model was evaluated in different configurations on the prediction of frequency effects on the Potsdam Sentence Corpus. The extension of EMMA with postlexical processing improved its predictions and reproduced re-reading rates and durations with a reasonable fit to the data. This demonstration, based on simple and independently motivated assumptions, serves as a foundational step toward a precise investigation of the interaction between high-level language processing and eye movement control.

In Persian, a construction exists in which a gap can optionally be replaced by an overt pronoun. A self-paced reading study (110 participants) suggests that the overt pronoun results in deeper encoding (higher activation) of the antecedent noun, presumably because of richer retrieval cue specifications during antecedent retrieval at the pronoun; this higher activation has the consequence that the antecedent is easier to retrieve at a subsequent stage. This provides new evidence for reactivation effects of the type assumed in the cue-based retrieval model of parsing (Lewis and Vasishth, 2005), and shows that dependency resolution is not simply a matter of connecting two co-dependents; the retrieval cue specification has a differential impact on processing.

Eye-movement research on implicit prosody has found effects of lexical stress on syntactic
ambiguity resolution, suggesting that metrical well-formedness constraints interact
with syntactic category assignment. Building on these findings, the present
eyetracking study investigates whether contextual bias can modulate the effects of
metrical structure on syntactic ambiguity resolution in silent reading. Contextual bias
and potential stress-clash in the ambiguous region were crossed in a 2 × 2 design.
Participants read biased context sentences followed by temporarily ambiguous test
sentences. In the three-word ambiguous region, main effects of lexical stress were
dominant, while early effects of context were absent. Potential stress clash yielded
a significant increase in first-pass regressions and re-reading probability across the
three words. In the disambiguating region, the disambiguating word itself showed
increased processing difficulty (lower skipping and increased re-reading probability)
when the disambiguation engendered a stress clash configuration, while the word
immediately following showed main effects of context in those same measures. Taken
together, effects of lexical stress upon eye movements were swift and pervasive across
first-pass and second-pass measures, while effects of context were relatively delayed.
These results indicate a strong role for implicit meter in guiding parsing, one that
appears insensitive to higher-level constraints. Our findings are problematic for
two classes of models, the two-stage garden-path model and the constraint-based
competition-integration model, but can be explained by a variation on the two-stage
model, the unrestricted race model.

What theories best characterize the parsing processes triggered upon encountering ambiguity, and what effects do these processes have on eye movement patterns in reading? The present eye-tracking study, which investigated processing of attachment ambiguities of an adjunct in Spanish, suggests that readers sometimes underspecify attachment to save memory resources, consistent with the good-enough account of parsing. Our results confirm a surprising prediction of the good-enough account: high-capacity readers commit to an attachment decision more often than low-capacity participants, leading to more errors and a greater need to reanalyze in garden-path sentences. These results emerged only when we separated functionally different types of regressive eye movements using a scanpath analysis; conventional eye-tracking measures alone would have led to different conclusions. The scanpath analysis also showed that rereading was the dominant strategy for recovering from garden-pathing. Our results may also have broader implications for models of reading processes: reanalysis effects in eye movements occurred late, which suggests that the coupling of oculo-motor control and the parser may not always be as tight as assumed in current computational models of eye movements control in reading.

Background: In behavioural tests of sentence comprehension in aphasia, correct and
incorrect responses are often randomly distributed. Such a pattern of chance performance
is a typical trait of Broca’s aphasia, but can be found in other aphasic syndromes as well.
Many researchers have argued that chance behaviour is the result of a guessing strategy,
which is adopted in the face of a syntactic breakdown in sentence processing.
Aims: Capitalising on new evidence from recent studies investigating online sentence comprehension
in aphasia using the visual world paradigm, the aim of this paper is to review
the concept of chance performance as a reflection of a syntactic impairment in sentence
processing and to re-examine the conventional interpretation of chance performance as a
guessing behaviour.
Main Contribution: Based on a review of recent evidence from visual world paradigm
studies, we argue that the assumption of chance performance equalling guessing is not
necessarily compatible with actual real-time parsing procedures in people with aphasia.
We propose a reinterpretation of the concept of chance performance by assuming that
there are two distinct processing mechanisms underlying sentence comprehension in
aphasia. Correct responses are always the result of normal-like parsing mechanisms, even
in those cases where the overall performance pattern is at chance. Incorrect responses, on
the other hand, are the result of intermittent deficiencies of the parser. Hence the random
guessing behaviour that persons with aphasia often display does not necessarily reflect a
syntactic breakdown in sentence comprehension and a random selection between alternatives.
Instead it should be regarded as a result of temporal deficient parsing procedures
in otherwise normal-like comprehension routines.
Conclusion: Our conclusion is that the consideration of behavioural offline data alone
may not be sufficient to interpret a performance in language tests and subsequently draw
theoretical conclusions about language impairments. Rather it is important to call on
additional data from online studies that look at language processing in real time in order
to gain a comprehensive picture about syntactic comprehension abilities of people with
aphasia and possible underlying deficits.

Shravan Vasishth, Rukshin Shaher, and Narayanan Srinivasan.
The role of clefting, word order and given-new ordering in
sentence comprehension: Evidence from Hindi.
Journal of South Asian Linguistics, 2012.
[ code |
pdf ]

Two Hindi eyetracking studies show that clefting a noun results in greater processing difficulty initially,
due to the extra processing steps involved in encoding a clefted noun (e.g., for computing the
exhaustiveness interpretation). However, this extra difficulty in encoding a clefted noun results in a
processing advantage when the clefted noun needs to be retrieved later on in the sentence - the clefted
noun is retrieved faster in subsequent processing compared to its non-clefted counterpart. This effect
is short-lived, however; it does not last beyond the current sentence. We also show that given-new
ordering yields a processing advantage over new-given order, but this is only seen after the whole
sentence is processed, i.e., it is a late effect that occurs after syntactic processing is completed. Finally,
following up on work on German by Hoernig et al. (2005), we present evidence that non-canonical order
can be processed more easily than canonical order given appropriate context.

Eye movement data have proven to be very useful for investigating human
sentence processing.Eyetracking research has addressed a wide range of questions,
such as recovery mechanisms following garden-pathing, the timing of processes
driving comprehension, the role of anticipation and expectation in parsing, the
role of semantic, pragmatic, and prosodic information, and so on. However, there
are some limitations regarding the inferences that can be made on the basis of eye
movements. One relates to the nontrivial interaction between parsing and the eye
movement control system which complicates the interpretation of eye movement
data. Detailed computational models that integrate parsing with eye movement
control theories have the potential to unpack the complexity of eyemovement data
and can therefore aid in the interpretation of eye movements. Another limitation
is the difficulty of capturing spatiotemporal patterns in eye movements using the
traditional word-based eyetracking measures. Recent research has demonstrated
the relevance of these patterns and has shown how they can be analyzed. In this
review, we focus on reading, and present examples demonstrating how eye movement
data reveal what events unfold when the parser runs into difficulty, and how
the parsing system interacts with eye movement control

Many comprehension theories assert that increasing the distance between elements participating in a
linguistic relation (e.g., a verb and a noun phrase argument) increases the difficulty of establishing that
relation during on-line comprehension. Such locality effects are expected to increase reading times and
are thought to reveal properties and limitations of the short-term memory system that supports comprehension.
Despite their theoretical importance and putative ubiquity, however, evidence for on-line
locality effects is quite narrow linguistically and methodologically: It is restricted almost exclusively to
self-paced reading of complex structures involving a particular class of syntactic relation. We present 4
experiments (2 self-paced reading and 2 eyetracking experiments) that demonstrate locality effects in the
course of establishing subject-verb dependencies; locality effects are seen even in materials that can be
read quickly and easily. These locality effects are observable in the earliest possible eye-movement
measures and are of much shorter duration than previously reported effects. To account for the observed
empirical patterns, we outline a processing model of the adaptive control of button pressing and eye
movements. This model makes progress toward the goal of eliminating linking assumptions between
memory constructs and empirical measures in favor of explicit theories of the coordinated control of
motor responses and parsing.

Eye fixation durations during normal reading correlate with processing difficulty,
but the specific cognitive mechanisms reflected in these measures are not well
understood. This study finds support in German readers‚Äô eye fixations for two
distinct difficulty metrics: surprisal, which reflects the change in probabilities
across syntactic analyses as new words are integrated; and retrieval, which
quantifies comprehension difficulty in terms of working memory constraints.We
examine the predictions of both metrics using a family of dependency parsers
indexed by an upper limit on the number of candidate syntactic analyses they
retain at successive words. Surprisal models all fixation measures and regression
probability. By contrast, retrieval does not model any measure in serial
processing. As more candidate analyses are considered in parallel at each word,
retrieval can account for the same measures as surprisal. This pattern suggests an
important role for ranked parallelism in theories of sentence comprehension.

While it is widely acknowledged in the formal semantic literature that both the truth-functional focus particle only and it-clefts convey exhaustiveness, the nature and source of exhaustiveness effects with it-clefts remain contested. Based on an event-related brain potentials (ERPs) study on only-foci and it-clefts, we provide experimental evidence that the violation or cancelation of exhaustive readings involve different underlying processes in the two structural environments.

Background: In addition to the canonical subject-verb-object (SVO) word order, German also allows for non-canonical order (OVS), and the case-marking system supports thematic role interpretation. Previous eye-tracking studies (Kamide et al., 2003; Knoeferle, 2007) have shown that unambiguous case information in non-canonical sentences is processed incrementally. For individuals with agrammatic aphasia, comprehension of non-canonical sentences is at chance level (Burchert et al., 2003). The trace deletion hypothesis (Grodzinsky 1995, 2000) claims that this is due to structural impairments in syntactic representations, which force the individual with aphasia (IWA) to apply a guessing strategy. However, recent studies investigating online sentence processing in aphasia (Caplan et al., 2007; Dickey et al., 2007) found that divergences exist in IWAs' sentence-processing routines depending on whether they comprehended non-canonical sentences correctly or not, pointing rather to a processing deficit explanation.
Aims: The aim of the current study was to investigate agrammatic IWAs' online and offline sentence comprehension simultaneously in order to reveal what online sentence-processing strategies they rely on and how these differ from controls' processing routines. We further asked whether IWAs' offline chance performance for non-canonical sentences does indeed result from guessing.
Methods & Procedures: We used the visual-world paradigm and measured eye movements (as an index of online sentence processing) of controls (N = 8) and individuals with aphasia (N = 7) during a sentence-picture matching task. Additional offline measures were accuracy and reaction times.
Outcomes & Results: While the offline accuracy results corresponded to the pattern predicted by the TDH, IWAs' eye movements revealed systematic differences depending on the response accuracy.
Conclusions: These findings constitute evidence against attributing IWAs' chance performance for non-canonical structures to mere guessing. Instead, our results support processing deficit explanations and characterise the agrammatic parser as deterministic and inefficient: it is slowed down, affected by intermittent deficiencies in performing syntactic operations, and fails to compute reanalysis even when one is detected.

Three experiments (self-paced reading, eyetracking and an
ERP study) show that in relative clauses, increasing the distance be
tween the relativized noun and the relative-clause verb makes it more
difficult to process the relative-clause verb (the so-called locality effect).
This result is consistent with the predictions of several theories (Gibson 2000, Lewis and Vasishth 2005), and contradicts the recent claim
(Levy 2008) that in relative-clause structures increasing argument-verb
distance makes processing easier at the verb. Levy's expectation-based
account predicts that the expectation for a verb becomes sharper as dis-
tance is increased and therefore processing becomes easier at the verb.
We argue that, in addition to expectation effects (which are seen in the
eyetracking study in first-pass regression probability), processing load
also increases with increasing distance. This contradicts Levy's claim
that heightened expectation leads to lower processing cost. Dependency-
resolution cost and expectation-based facilitation are jointly responsible
for determining processing cost.

Which repair strategy does the language system deploy when it gets
garden-pathed and what can regressive eye movements in reading tell us about
reanalysis strategies? Several influential eye-tracking studies on syntactic
reanalysis (Frazier & Rayner 1982, Meseguer et al 2002, Mitchell et al 2008) have
examined scanpaths-sequences of eye fixations-to answer this question.
However, in the absence of a suitable method for analyzing scanpaths, these studies
relied on simplified dependent measures that are arguably ambiguous and hard to
interpret. We address the theoretical question of repair strategy by developing
a new method that quantifies scanpath similarity. Our method reveals several
distinct fixation strategies associated with reanalysis that went undetected in
a previously published data set (Meseguer et al 2002). One prevalent pattern
suggests re-parsing of the sentence, a strategy that has been proposed in the
literature (Frazier & Rayner 1982); however, readers differed tremendously in
how they orchestrated the various fixation strategies. Our results raise the
possibility that the human parsing system non-deterministically adopts different
strategies when confronted with the need to reanalyze.

Seven experiments using self-paced reading and eyetracking suggest that omitting the middle verb in a double centre embedding leads to easier processing in English but leads to greater difficulty in German. One commonly accepted explanation for the English pattern‚Äîbased on data from offline acceptability ratings and due to Gibson and Thomas (1999)‚Äîis that working-memory overload leads the comprehender to forget the prediction of the upcoming verb phrase (VP), which reduces working-memory load. We show that this VP-forgetting hypothesis does an excellent job of explaining the English data, but cannot account for the German results. We argue that the English and German results can be explained by the parser's adaptation to the grammatical properties of the languages; in contrast to English, German subordinate clauses always have the verb in clause-final position, and this property of German may lead the German parser to maintain predictions of upcoming VPs more robustly compared to English. The evidence thus argues against language-independent forgetting effects in online sentence processing; working-memory constraints can be conditioned by countervailing influences deriving from grammatical properties of the language under study.

This paper presents the results of an experimental study on multiple focus
configurations, that is, structures containing two nested focus-sensitive operators
plus two foci supposed to associate with those operators. There has been controversial
discussion in the semantic literature regarding whether or not an interpretation is
acceptable that corresponds to this association. While the data are unclear, the issue is
of considerable theoretical significance, as it distinguishes between the available
theories of focus interpretation. Some theories (e.g. Rooth, 1992) predict such
a pattern of association with focus to be impossible, while others (such as Wold,
1996) predict it to be acceptable. The results of our study show the data to be
unacceptable rather than acceptable, favouring important aspects of the theory of
focus interpretation developed by Rooth.

A production study is presented that investigates the effects of word order and information structural
context on the prosodic realization of declarative sentences in Hindi. Previous work on Hindi intonation
has shown that: (i) non-final content words bear rising pitch accents (Moore 1965, Dyrud 2001, Nair
1999); (ii) focused constituents show greater pitch excursion and longer duration and that post-focal
material undergoes pitch range reduction (Moore 1965, Harnsberger 1994, Harnsberger and Judge
1996); and (iii) focused constituents may be followed by a phrase break (Moore 1965). By means of
a controlled experiment, we investigated the effect of focus in relation to word order variation using
1200 utterances produced by 20 speakers. Fundamental frequency (F0) and duration of constituents
were measured in Subject-Object-Verb (SOV) and Object-Subject-Verb (OSV) sentences in different
information structural conditions (wide focus, subject focus and object focus). The analyses indicate
that (i) regardless of word order and focus, the constituents are in a strict downstep relationship;
(ii) focus is mainly characterized by post-focal pitch range reduction rather than pitch raising of the
element in focus; (iii) given expressions that occur pre-focally appear to undergo no reduction; (iv)
pitch excursion and duration of the constituents is higher in OSV compared to SOV sentences. A
phonological analysis suggests that focus affects pitch scaling and that word order influences prosodic
phrasing of the constituents.

The surprisal of a word on a probabilistic grammar constitutes a promising
complexity metric for human sentence comprehension difficulty. Using two
different grammar types, surprisal is shown to have an effect on fixation durations
and regression probabilities in a sample of German readers' eye movements, the
Potsdam Sentence Corpus. A linear mixed-effects model was used to quantify the
effect of surprisal while taking into account unigram frequency and bigram frequency
(transitional probability), word length, and empirically-derived word predictability;
the so-called ‚“early” and “late” measures of processing difficulty both showed
an effect of surprisal. Surprisal is also shown to have a small but statistically
non-significant effect on empirically-derived predictability itself. This work thus
demonstrates the importance of including parsing costs as a predictor of comprehension
difficulty in models of reading, and suggests that a simple identification
of syntactic parsing costs with early measures and late measures with durations of
post-syntactic events may be difficult to uphold.

A central question in online human sentence comprehension is: how are linguistic
relations established between different parts of a sentence? Previous work has shown that
this dependency resolution process can be computationally expensive, but the underlying
reasons for this are still unclear. We argue that dependency resolution is mediated by
cue-based retrieval, constrained by independently motivated working memory principles
defined in a cognitive architecture (ACT-R). To demonstrate this, we investigate an
unusual instance of dependency resolution, the processing of negative and positive
polarity items, and confirm a surprising prediction of the cue-based retrieval model:
partial cue-matches, which constitute a kind of similarity-based interference, can give
rise to the intrusion of ungrammatical retrieval candidates, leading to both processing
slow-downs and even errors of judgment that take the form of illusions of grammaticality
in patently ungrammatical structures. A notable achievement is that good quantitative
fits are achieved without adjusting the key model parameters.

Understanding a sentence requires a working memory
of the partial products of comprehension, so that
linguistic relations between temporally distal parts of
the sentence can be rapidly computed. We describe an
emerging theoretical framework for this working
memory system that incorporates several independently
motivated principles of memory: a sharply limited
attentional focus, rapid retrieval of item (but not order)
information subject to interference from similar items,
and activation decay (forgetting over time). A computational
model embodying these principles provides an
explanation of the functional capacities and severe
limitations of human processing, as well as accounts
of reading times. The broad implication is that the
detailed nature of crosslinguistic sentence processing
emerges from the interaction of general principles of
human memory with the specialized task of language
comprehension.

We present a detailed process theory of the moment-by-moment working-memory retrievals and associated
control structure that subserve sentence comprehension. The theory is derived from the application
of independently motivated principles of memory and cognitive skill to the specialized task of sentence
parsing. The resulting theory construes sentence processing as a series of skilled associative
memory retrievals modulated by similarity-based interference and fluctuating activation. The cognitive
principles are formalized in computational form in the Adaptive Control of Thought-Rational (ACT-R)
architecture, and our process model is realized in ACT-R.We present the results of 6 sets of simulations:
5 simulation sets provide quantitative accounts of the effects of length and structural interference on
both unambiguous and garden-path structures. A final simulation set provides a graded taxonomy of
double center embeddings ranging from relatively easy to extremely difficult. The explanation of center-
embedding difficulty is a novel one that derives from the model‚Äôs complete reliance on discriminating
retrieval cues in the absence of an explicit representation of serial order information. All fits were obtained
with only 1 free scaling parameter fixed across the simulations; all other parameters were ACT-R
defaults. The modeling results support the hypothesis that fluctuating activation and similarity-based interference
are the key factors shaping working memory in sentence processing. We contrast the theory
and empirical predictions with several related accounts of sentence-processing complexity.

Discourse context has been argued to be the main factor responsible for increased processing difficulty in non-canonical order sentences: if appropriate discourse context is provided (the argument goes) both canonical and non-canonical order sentences are equally easy to process. This research suggests that this generalization may not be true across languages: the distance between arguments and verbs could affect the ease with which the former can be integrated with the latter, and sufficiently increasing this distance makes processing difficult, regardless of discourse context.

In Hindi certain word order possibilities that are grammatical in non-negative sentences
become ungrammatical in the presence of sentential negation. In movement-based accounts of such
negation-induced word order constraints, the restricted word order has been argued to provide
evidence that negative polarity items (NPIs) in Hindi are licensed at LF and S-structure while in
English NPI licensing occurs at S-structure. I argue for a non-movement-based, uniformly monostratal
(S-structure) account for the word order facts in Hindi, cast in the multimodal categorial
grammar framework. The NPI licensing issue is dealt with independently following Dowty's
monotonicity marking analysis.

This is the first attempt at characterizing reading difficulty in Hindi in naturally occurring sentences. We created the Potsdam-Allahabad Hindi Eyetracking Corpus by recording eye-movement data from 30 participants at the University of Allahabad, India. The target stimuli were 153 sentences selected from the beta version of the Hindi-Urdu treebank. We find that word or low-level predictors (word length, unigram and bigram frequency) affect first-pass reading times, regression path duration, total reading time, and outgoing saccade length, An increase in word length results in longer fixations, and an increase in word unigram and bigram frequency results in shorter fixations. Longer word length led to longer outgoing saccades, and higher frequency (unigram and bigram) also led to longer outgoing saccades. We also find that two predictors of sentence comprehension difficulty, integration and storage cost (computed based on Dependency Locality Theory, Gibson, 2000) affect regression path duration, total reading time, and outgoing saccade length. Integration cost is approximated by calculating the distance (in words) between a dependent and head; and storage cost measures difficulty of maintaining predictions by counting the number of predicted heads at each point in the sentence. Thus, word-level predictors have an effect in both early and late measures of reading time, while predictors of sentence comprehension difficulty affect later measures, suggesting that classical psycholinguistic measures of working memory difficulty have strong effects on fixation measures in reading.

SOPARSE (Tabor & Hutchins, 2004) predicts so-called local coherence effects: locally plausible but globally impossible parses of substrings can exert a distracting influence during sentence processing. Additionally, it predicts digging-in effects: the longer the parser stays committed to a particular analysis, the harder it becomes to inhibit that analysis. We investigated the interaction of these two predictions using German sentences. Results from a self-paced reading study show that the processing difficulty caused by a local coherence can be reduced by first allowing the globally correct parse to become entrenched, which supports SOPARSE’s assumptions.

How important is the ability to freely control eye movements for reading comprehension? We
investigated this question using event-related brain potentials recorded while participants read
either word-by-word (also known as RSVP) or naturally. Additionally, eye movements were
recorded concurrently with brain potentials during natural reading. Word-by-word presentation
and natural reading both elicited similar N400 and P600 effects in response to syntactic and
semantic violations. However, comprehension accuracy was higher in natural reading than in
word-by-word presentation and particularly high when participants regressed to earlier portions
of the sentence after encountering the violation. A more fine-grained ERP analysis showed that
P600 effects, which are believed to reflect recovery processes, only occurred in trials with
regressive eye movements. In trials without regressions, we instead found either a sustained,
centro-parietal negativity starting at around 320 ms post-onset or no effect depending on the
position of the violation within the sentence. Thus, the combined analysis of eye movements and
ERPs reveals that the sentence comprehension system engages in strategic choices when
confronted with difficult material and that the ability to reread earlier parts of the sentence is the
key to thorough comprehension.

With the arrival of the R packages nlme and lme4,
linear mixed models (LMMs) have come to be widely used in psychology, cognitive science, and related areas. In this tutorial, we provide a practical introduction to fitting LMMs in a Bayesian framework using the probabilistic programming language Stan. Although the Bayesian framework has several important advantages, specifying a Bayesian model requires quite a lot of background knowledge compared to frequentist tools like lme4. This tutorial provides the necessary background through two detailed examples of self-paced reading studies with repeated measures. One is a two-condition design, and the other a 2×2 factorial design. These two examples can easily be extended to more complex factorial designs.
The data and code associated with this tutorial are available as a supplement.

Bruno Nicenboim, Shravan Vasishth, and Reinhold Kliegl.
Readers with less cognitive control are more affected by
surprising content.
In Architectures and Mechanisms for Language Processing
(AMLaP), September 2014.

Bruno Nicenboim, Pavel Logačev, Carolina Gattei, and Shravan Vasishth.
When high-capacity readers slow down and low-capacity readers
speed up: Working memory differences in unbounded dependencies for German
and Spanish readers.
In Mental Architecture for Processing and Learning of Language
(MAPLL), August 2014.

Bruno Nicenboim, Shravan Vasishth, and Reinhold Kliegl.
Readers with less cognitive control are more affected by
surprising content: Evidence from a self-paced reading experiment in
German.
In Mental Architecture for Processing and Learning of Language
(MAPLL), August 2014.
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